A network of 80 branches, a routing issue?

Question

openvpn

Tell me there are several networks at the head office (192.168.0.0, 192.168.1.0, 192.168.2.0, etc.).
From the side of the main office there is an OpenVPN server, to which people on personal and home laptops will connect.
Now there is a network of stores with about 80 pieces, where Asus RT n56u, several laptops, about 5 IP cameras are installed from the equipment.
The goal is to combine them into one network, apply security policies including AppLocker, monitor cameras via Zabbix, as well as monitor the online status of each store, and there are little things like Windows counters.
In general, the task is not difficult, we flash the Asus RT-N56U router with firmware from Padavan, after which it becomes possible to configure it as an OpenVPN client. All remote network can go to the parent and back.
But what to do with DNS? Any FQDN request that is not an IP address is sent by the router to external DNS servers. You can configure DNS queries to go through OpenVPN, receive a response that the internal server is sent to it, if the external one then the request goes back to the branch network, to the laptop and back to the Internet. Then DNS responses are received with too much delay. How to be? it is clear that it is easier to put DNS in each office and not bother, but there is no way! The equipment moves regularly and work is needed according to this scheme. What will be the proposals?

Answer 1

Add the main dns suffix to all names (server.mycompany.com) and for mycompany.com create an NS record with your internal DNS IP
FQDN query vasya.mycompany.com will resolve your internal server and for example mail.ru - external
will split by branches server.filial-1.mycompany.com server.filial-2.mycompany.com server.filial-n.mycompany.com
This is the direction in which you can solve the issue, if I correctly caught your problem

Answer 2

Set DNS inside the network, set up an internal domain. On the network equipment, write down the IP of the internal DNS.